Solid hard metal head for a drill

ABSTRACT

A solid hard metal head for a drill, including two main cutting edges ( 2 ) arranged substantially diametrially opposite each other, and two auxiliary cutting edges ( 3 ) likewise arranged substantially diametrically opposite each other, with associated main cutting edge ( 2 ) and auxiliary cutting edge ( 3 ) form an acute angle (α) there between, and with the auxiliary cutting edges ( 3 ) being arranged, with respect to the rotational direction (ω) of the drill, in front of the respective, associated therewith, main cutting edge ( 2 ).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a solid hard metal head for a rock drill used for drilling stones and concrete and securable in mechanized hand-held tools for removal abrasive materials upon application of a rotary percussion movement thereto.

[0003] 2. Description of the Prior Act

[0004] Drills for drilling in stone or concrete require, because they are used for removal of abrasive materials, that the parts insertable into the drill head be made of hard metal as they should have a high hardness so that they would not be subjected to an extensive wear. The insertable parts are fixedly secured in the drill. Usually, the insertable parts are formed as hard metal plates soldered in the head. Such a drill is disclosed in German document DE 20 08 825. A relatively small flexural strength of the heard metal plates leads to their breaking out of the remainder of the drill, in particular, when the drill head encounters a reinforcing metal.

[0005] German Publication DE 43 39 245 discloses forming an entire drill head of a hard metal as a solid hard metal head. A solid hard metal head has a compact, substantially convex, polygonal shape with the lengths of its sides being substantially the same. Due to this shape, the solid hard metal head has a high inner stiffness. To prevent the main cutting edges from hooking in reinforcing metal, usually, auxiliary cutting edges are provided between the main cutting edges and which are arranged exclusively on the radial edge of the head and are axially offset. The auxiliary cutting edges, due to their penetration resistance and mass inertia, prevent the main cutting edges from penetrating deeply into the reinforcing metal by temporary lifting the drill from the reinforcing metal. The manufacturing and economical drawbacks of this drill result from a large volume of the solid hard metal head when the drill is designed for drilling large-diameter bores.

[0006] In addition, it is anticipated that the auxiliary cutting edge would have a slightly concave, in the axial direction, shape with an obtuse angle being formed in a plane, which passes through the radially outer cutting edges transvers to the drill rotational axis, with the obtuse angle being symmetrical with respect to the rotational axis. The concave, in the axial direction, shape of the auxiliary cutting edge, in cooperation with the non-concave main cutting edge, forms an axially extending free space for removal of drillings from the tool tip and which prevents compression of the drillings in front of the drill tip which otherwise would have reduced the drill performance. The drawback of forming the auxiliary cutting edges with a slightly concave shape consists in that the auxiliary cutting edges, in combination with a non-concave main cutting edges, make precise drilling more difficult.

[0007] German Publication DE 19 70 711.5 discloses a drill having a one-piece, prismatic, solid hard metal head with more than two rotationally symmetrical, radial cutting edges and which is inserted in corresponding grooves formed in the drill body and having axially extending surfaces, with the head being fixedly secured with the drill body along the axially extending surfaces of the groove and to the end surface of the drill body. The attachment of the head to the end surface of the drill body, on one hand, and the additional securing of the head, in the radially outer region of the head, in the axial grooves with formation mortise and tenon joints, on the other hand, provides for a breakproof securing of the cutting edges, even in large diameter drills, so that they would not be dislodged even upon engagement with the reinforcing metal. However, with increased number of cutting edges, with the same available power, a smaller force is applied to each edge, which adversely affects drill performance. Another drawback of the above-described rill consists in a need to form a plurality of mortises corresponding to the number of the cutting edges, this makes solving the problem of removing of the drilled abrasive material more difficult.

[0008] European publication EP 88 44 48 discloses a solid hard metal head with an “X”-shaped arrangement of four cutting edges, with the main cutting edges and the auxiliary cutting edges, which are formed as side cutting edges, being arranged, respectively, diametrically opposite each other and with respective main and auxiliary cutting edges forming an angle that deviates from 90°. The main cutting edges form, in their plane, an obtuse angle, with the tip being in the region of the rotational axis. The auxiliary cutting edges extend perpendicular to the rotational axis and are axially offset backward in such a way that the inner region of a bore is cut with main cutting edges, and the outer region of the bore is cut with the auxiliary, side, cutting edges. The so formed side cutting edges have a tendency to break upon striking a reinforcing metal, as a result of a high load applied to the side edges.

[0009] The “X”-shaped, solid, hard metal head has essentially a rotationally symmetrical, crosswise, axially mirror symmetrical, prismatic shape. The base surface is provided with deep, concave, obtuse-angled notches which extend radially inward along one-third of the base surface parallel to the cutting edges over the longer surfaces. The notches serve for removal of the cut abrasive material. The side cutting edges trail the main cutting edges in the rotational direction, forming with the respective main cutting edges acute angles. As a result, a large recess is provided in front of a main cutting edge. A small concave recess on each of the short sides of the base surface is limited by the radial edge region and serves for removal of some of the cut abrasive material in front of the respective auxiliary or side cutting edge. The drawback of this head consists in that because of an obtuse angle, in the rotational direction, between the auxiliary cutting edge and the trailing main cutting edge, a large rotational angle is needed in order to overcome the mass inertia.

[0010] However, practically, it is impossible to provide for such angle in low-speed large-diameter drills.

[0011] Accordingly, an object of the present invention is to provide a solid hard metal head for a rock drill which would insure, even with a large head diameter, application of high localized forces to the cutting edges for achieving a high drilling capacity.

[0012] Another abject of the present invention is to provide a solid hard metal head for a rock drill which would insure adequate removal of the cut abrasive material and a precise spot drilling.

[0013] A further object of the present invention is to provide a solid hard metal head for a rock drill which would insure application of a reduced load to the cutting edges upon encounter of the drilling head with reinforcing metal.

[0014] A still further object of the present invention is to provide a solid hard metal head for a rock drill with break-proof cutting edges.

SUMMARY OF THE INVENTION

[0015] This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a solid hard metal head for a drill including two main cutting edges arranged substantially diametrically opposite each other, and two auxiliary cutting edges likewise arranged substantially diametrically opposite each other, with associated main cutting edge and auxiliary cutting edge forming an acute angle therebetween, and with the auxiliary cutting edges being arranged, with respect to the rotational direction of the drill, in front of the respective, associated therewith, main cutting edges.

[0016] Advantageously, the inventive solid hard metal head has a drilling diameter from 12 mm to 40 mm. The arrangement of the auxiliary cutting edges in front of the main cutting edges provides for lifting of the drill when the drill strikes reinforcing metal, which prevents application of a load to the main cutting edges when the drill strikes reinforcing metal. The acute angle between the associated main and auxiliary cutting edges, which lies in a plane extending transverse to a drill rotational axis, lies in a range between 40° and 90°. Thus, for overcoming mass inertia, only a small rotational angle need be bridged.

[0017] A satisfactory removal of the cut abrasive material in front of main cutting edge into a helical groove adjoining the solid hard metal head of the drill is insured by providing between adjacent cutting edges two radial concave recesses, respectively, extending parallel to the respective edges and formed in the circumference of the cross-sectional surface and having a prismatic shape in the axial direction. A portion of a side surface of the recess, which extends along the rotational axis, advantageously, in front of the auxiliary cutting edge, provides for additional securing of the solid hard metal head in groove-shaped tenons provided in the tool body. These portions of the side surfaces advantageously are provided with chamfers extending toward the end surface for breaking the edge. The foregoing structure insures a break-proof attachment of the solid hard metal head to the drill body and provides for pressure-side support of the main cutting edges. Providing, advantageously, a groove in the drill body, which is associated with the diametrically opposite recesses, insures self-centering of the solid hard metal head when it is being attached to the drill body.

[0018] Advantageously, the main cutting edges are so formed that they end, at the tip of the head, at a chisel edge and have a slightly concave shape, whereby a somewhat acute angle is formed with respect to the tip region, which provides for precise spot drilling with the chisel edge, and a somewhat obtuse angle is formed between the main cutting edges and the rotational axis with respect to the radial outer region, which provides for a precisely axial lead-in of the axial blows imparted to the drill, which insures transmittal of the energy of axial blows to the cut material with minimum losses. Advantageously, the auxiliary cutting edges have a pronounced axially concave shape, therefore, a plane, which passes through the radial outer regions of the auxiliary cutting edges perpendicular to the rotational axis, is interrupted. Thus, in combination with slightly axially concave shape of the main cutting edges, there are provided axial recesses which insure removal of the cut material from the drill (head) tip.

[0019] A transitional surface in a sector between adjacent main and auxiliary cutting edges has advantageously a circumferentially concave shape in an axial direction, which permits to obtain a larger recess for transporting drillings and to obtain a high inner stiffness of the solid hard metal head.

[0020] Forming the main and the auxiliary cutting edges as integral arts of the solid hard metal head insures their precise positioning relative to each other, which is not affected by manufacturing tolerances associated with attachment of the head with the drill body. In order to obtain a low vibration operation of the drill, the axial spacing of the auxiliary cutting edges is so selected that the highest point of the axial generating curve does not project exactly over the axial generating curve of the main cutting edges. A low-vibration operation and a uniform round bore geometry is achieved by matching the generating envelopes of the main and auxiliary cutting edges to each other, in particular, by an appropriate radial displacement of the generating curve of the auxiliary cutting edges relative to the main cutting edges.

[0021] The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings show:

[0023]FIG. 1 a perspective view of the solid hard metal head of a drill according to the present invention;

[0024]FIG. 2 a plan view of the solid hard metal head shown in FIG. 1;

[0025]FIG. 3 a side view of the solid hard metal head shown in FIG. 1; and

[0026]FIG. 4 an angular side view of the solid hard metal head shown in FIG. 1

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0027] A solid hard metal head 1 of a drill according to the present invention, which is shown in FIG. 1, has advantageously a drilling diameter from 12 mm to 40 mm and an X-shaped arrangement of four cutting edges 2, 3, with the main cutting edges 2 extending diametrically opposite each other with respect to the rotational axis A, and with respective main cutting edge 2 and auxiliary cutting edge 3 forming an angle that deviates from 90°, namely, an acute angle. The auxiliary cutting edge 3 is arranged, in the drill rotational direction ω, in front of the associated therewith, main cutting edge 2.

[0028] According to FIG. 2, an angle α between the main cutting edge 2 and the auxiliary cutting edge 3, which lies in plane extending perpendicular to the rotational axis A, amounts to or is located within a range from 40° to 90°. With respect to the generating curve of the main cutting edge 2, the auxiliary cutting edge 3 is radially displaced. Between two respective adjacent cutting edges 2, 3, there are provided two concave recesses 4, 5 formed in the circumference of the cross-sectional surface and having, in the axial direction, a substantially prismatic shape. A portion of a side surface 6 of the recess 5, which extends along the rotational axis A, advantageously, in front of the auxiliary cutting edge 3, provides for additional securing of the solid hard metal head 1 in mortises provided in the tool body.

[0029] As shown in FIG. 3, the securing portion of the side surface 6 has a chamfer 7 extending toward an end surface 8 for breaking the edge. The main cutting edge 2 which, at the tip, ends at chisel edge 9, has a slightly concave shape in the axial direction. The axial spacing of the auxiliary cutting edge 3 does not project exactly over the axial generating curve of the main cutting edge 2.

[0030] As shown in FIG. 4, the auxiliary cutting edge 3 has a noticeable concave shape in the axial direction, so that a plane 10, which extends through the radially outer regions of the auxiliary cutting edges 3 transverse to the rotational axis, is interrupted or cut. The pronounced concave shape of the auxiliary cutting edge 3, in cooperation with the slightly concave shape of the main cutting edge, forms a recess 11 for removal of drillings from the drill tip. The transition surface 12, in the sector between the adjacent cutting edges 2, 3, also has, in the axial direction, a circumferentially concave shape.

[0031] Though the present invention was shown and described with references to the preferred embodiments, such embodiments are merely illustrative of the present invention and are not to be construed as a limitation thereof, and various modifications of the present invention will be apparent to those skilled in the art. It is, therefore, not intended that the present invention be limited to the disclosed embodiments or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims. 

What is claimed is:
 1. A solid hard metal head for a drill, comprising two main cutting edges (2) arranged substantially diametrically opposite each other, and two auxiliary cutting edges (3) likewise arranged substantially diametrically opposite each other, wherein associated main cutting edge (2)and auxiliary cutting edge (3) form an acute angle (α) therebetween, and wherein the auxiliary cutting edges (3) are arranged, with respect to the rotational direction (ω) of the drill, in front of the respective, associated therewith, main cutting edges (2).
 2. A solid hard metal head according to claim 1 , wherein the acute angle (α) between the associated main and auxiliary cutting edges (2; 3), which lies in a plane extending transverse to a drill rotational axis, lies in a range between 40 and 90°.
 3. A solid hard metal head according to claim 1 , wherein a recess (4; 5) is formed between each two adjacent main and auxiliary cutting edges (2; 3) in a circumference of a cross-sectional surface, and wherein the recess (4; 5) has somewhat prismatic shape and extends along an entire axial extent of the head (1).
 4. A solid hard metal head according to claim 3 , wherein a portion of a side surface (6) of the recess (5), which is arranged, with respect to the rotational direction (ω), in front of a respective auxiliary cutting edge (3) and extends in an axial direction along the rotational axis (A), has a chamfer (7) at an end surface of the head (8).
 5. A solid hard metal head according to claim 1 , wherein at the tip, the main cutting edge (2) ends at a chisel edge (9).
 6. A solid hard metal head according to claim 1 , wherein the main cutting edges (2) have, in an axial direction, a slightly concave shape.
 7. A solid hard metal head according to claim 1 , wherein the auxiliary cutting edges (3) have, in an axial direction, a pronounced concave shape.
 8. A solid hard metal head according to claim 1 , wherein an axial spacing of the auxiliary cutting edges (3) is so selected that a highest point of a generating curve of the auxiliary cutting edges (3) does not project above an axial generating curve of the main cutting edges.
 9. A solid hard metal head according to claim 1 , wherein the auxiliary cutting edges (3) are radially displaced with respect to a generating curve of the main cutting edges (2).
 10. A solid hard metal head according to claim 1 , wherein a transitional surface (12), in a sector between adjacent main and auxiliary cutting edges (2; 3), has a circumferentially concave shape in an axial direction. 